We present experimental evidence of polarization storage by nonlinear orientational hole burning in films of poly(methylmethacrylate) containing disperse red one (DR1). The data are written by polarized nonlinear excitation of DR1 by a tightly focused Ti: Sapphire laser and read by polarized confocal laser scanning microscopy in the reflection mode. The bits that are imaged with a light polarization which is parallel to the excitation laser polarization reflect light times more efficiently than those which are imaged with a light polarization which is perpendicular to it. This finding is consistent with orientational hole burning of chromophores by two-photon excitation.

We demonstrate the fabrication of superprism devices in photonic crystal waveguides with excellent transmission through 600 rows of diameter holes. Broadband spectral and angular measurements allow mapping of the chromatic refractivity. This shows the ability of such devices to super-refract by more than close to the principal band gaps, more than equivalent gratings, and more than equivalent prisms. Simple theories based on plane-wave models give excellent agreement with these results.

We report on the pressure dependence of the threshold current in and quantum-well lasers measured at low temperatures. It was found that the threshold current of both devices slowly increases with increasing pressure (i.e., increasing band gap) at consistent with the calculated variation of the radiative current. In contrast, at room temperature we observed a reduction of the threshold current with increasing pressure. Our low-temperature,high-pressure data confirm the results of previous atmospheric pressuremeasurements on the same devices which indicated a transition in the dominant recombination mechanism from radiative to Auger as the device temperature is increased from to .

An electrically tuned nematic liquid-crystal(LC) infiltrated photonic crystal(PC) laser is demonstrated. This PC laser represents an emerging class of nanoscale optical adaptive devices enabled by the convergence of nonlinear optical materials, electronics, and fluidics that promise increased functionality and utility over existing technologies. A LC cell is constructed by encasing the PC laser between two indium tin oxide glass plates, which serve as the modulating electrodes. Applying a voltage across the cell realigns the LC, modifies the laser cavity’s optical path length, and blueshifts the lasing wavelength.

We report full-field, retroreflective holographicimaging through turbid media using a photorefractive polymer composite as a coherence gate. A four-wave mixing geometry was used to record and reconstruct two-dimensional images of test objects through 6.5 scattering mean-free-paths in real-time. Images with a transverse spatial resolution better than were acquired in a few seconds using a helium neon laser at . The photorefractive devices used are based on a poly (-vinylcarbazole) (PVK):2,4,7-trinitro-9-fluorenone dimalenitrile (TNFDM) charge transport network, doped with the electro-optic chromophore , (EHDNPB).

We observed an orientational photorefractive effect in porphyrin:-doped nematic liquid crystals by measuring two beam coupling gain and diffraction efficiency under the influence of applied electric field. The gain and diffraction efficiency curves against applied electric field typically reveal resonant type curves, rapidly increasing to its maximum values and then gradually decreasing, but have clearly distinct peak positions. Based on the material equations and the torque balance equation of director axis reorientation of liquid crystals, we theoretically derived the expressions for the orientational photorefractive gain and diffraction efficiency, showing good agreement with the experimental results.

A fully microscopic model based on generalized quantum Bolzman equations for electron–electron and electron–phonon scattering is used to calculate the carrier capture dynamics in quantum-well lasers. The capture time and dynamics are governed by transitions between quantum states that are delocalized throughout the whole structure. Good agreement with experimental results is demonstrated for - and -based multi-quantum-well systems.

We report abnormally large positive and negative lateral optical beam shifts at a metal–air interface when the surface plasmon resonance of the metal is excited. The optimal thickness for minimal resonant reflection is identified as the critical thickness above which a negative beam displacement is observed. Experimental results show good agreement with theoretical predictions and the large observed bidirectional beam displacements also indicate the existence of forward and backward surface propagating waves at the surface plasmon resonance of the metal.

The domain wall regions in periodically poled crystals were examined and found to give rise to phasematched second harmonic generation in the Čerenkov directions. This phenomenon is caused by the nonlinear coefficients and , which are not present in single domain regions, but are nonzero at and close to domain walls. The appearance of these nonlinearities is attributed to strain, produced by the domain inversion process and results in the creation of a dcpiezoelectric field.

The nanoindentation-induced amorphization in is studied using molecular dynamics simulations. The load-displacement response shows an elastic shoulder followed by a plastic regime consisting of a series of load drops. Analyses of bond angles, local pressure, and shear stress, and shortest-path rings show that these drops are related to dislocation activities under the indenter. We show that amorphization is driven by coalescence of dislocation loops and that there is a strong correlation between load-displacement response and ring distribution.

We observe a dramatic enhancement of the fluorescence intensity from single core∕shell nanocrystals upon sudden exposure to air from an evacuated surrounding. Both the number of particles contributing to emission increases as well as the average emission intensity from a single particle, leading to an overall fluorescence rise by a factor of 60. A common power-law distribution of both on- and off times of single nanocrystals is observed independent of shell thickness and environment. We propose that electron transfer to oxygen, which is facilitated by the presence of water, leads to a neutralization of charged, nonemissive nanocrystals.

Acceptors in liquid encapsulated Czochralski-grown undoped gallium antimonide(GaSb) were studied by temperature dependent Hall measurement and positron lifetime spectroscopy (PLS). Because of its high concentration and low ionization energy, a level at is found to be the important acceptor responsible for the -type conduction of the samples. Two different kinds of -related defects (lifetimes of and , respectively) having different microstructures were characterized by PLS. By comparing their annealing behaviors and charge state occupancies, the level could not be related to the two -related defects.

We found that CaSi reversibly absorbs and desorbs hydrogen. First-principles calculationstheoretically indicated that CaSi hydride is thermodynamically stable. The hydriding and dehydriding properties of CaSi were experimentally determined using pressure-composition isotherms and x-ray diffraction analysis. The isotherms clearly demonstrated plateau pressures in a temperature range of . The maximum hydrogen content was under a hydrogen pressure of at . The reversible hydriding and dehydriding properties of CaSi suggest the potential of metal silicides for hydrogen storage.

The dynamic competition between structural transformation, Newtonian viscous flow, and anisotropic strain generation during ion irradiation of , leads to strongly depth-dependent evolution of the mechanical stress, ranging between compressive and tensile. From independent in situ stress measurements during irradiation, generic expressions are derived of the nuclear stopping dependence of both the structural transformation rate and the radiation-induced viscosity. Using these data we introduce and demonstrate the concept of a “stress map” that predicts the depth-resolved saturation stress in for any irradiation up to several MeV.

Ab initio calculations of the basic properties of solids have advanced significantly, and it is now possible to simply access a crystal structuredatabase, and from the given constituent atoms and their positions, calculate reasonably accurate values for elastic constants and thermomechanicalproperties that may be derived from them. However, progress has been impeded by a unique discrepancy involving the sign of one of the elastic constants of an important material: . In this letter, this longstanding discrepancy is resolved with experimental measurements.

The morphology of nanocermet thin films, prepared by cosputtering and on float glass substrates, was studied using surface sensitive x-ray scattering techniques and the results were correlated with the optical absorption of the films measured using ultraviolet visible spectroscopy. The presence of goldnanoparticles in an alumina matrix is evident from both x-ray scattering and spectroscopic studies. The distribution of nanoparticles is obtained from grazing incidence small angle x-ray scattering, while the electron density profile obtained from the analysis of x-rayreflectivity data gives total film thickness, volume fraction of and the special arrangement along the growth direction. Optical properties show a linear dependence of the absorption peak position with , which is interesting for making nanocomposites of tunable absorption.

Organic molecular-beam deposition of pentacene on gold substrates has been investigated using a multitechnique approach. The morphology of the organic thin films depends strongly on the substrate temperature. Pronounced dewetting and island formation are observed at room temperature. Whereas pentacene molecules adopt a planar monolayerstructure, they continue to grow in an upright orientation in multilayerfilms as inferred from x-ray absorption spectroscopy and atomic force microscopy. These results are in pronounced contrast to a recent scanning tunneling microscopy(STM) study by Kang and Zhu [Appl. Phys. Lett.82, 3248 (2003)] and indicate fundamental problems in the interpretation of STM measurements for organic thin films.

three period multiquantum green-light-emitting diodes(LEDs) grown by the metalorganic chemical vapor deposition technique have been studied using high-resolution transmission electron microscopy (HRTEM), double crystal high resolution x-ray diffraction (HRXRD) and low temperature photoluminescence. HRTEM analysis showed that the defect density gradually decreased in the growth direction with increasing thickness. Self-assembled quantum dot-likestructures in the wells and black lumps between the well and barrier due to segregation and strain contrast were observed, respectively. The HRXRD spectrum of the green LEDstructure was simulated using the kinematical theory method to obtain the composition and thickness of the well and barrier. The quantum-well (QW) green emission peak at showed “S” shaped shift like a red–blue–red shift with variation of the temperature in the photoluminescence spectra due to potential fluctuations caused by inhomogeneous alloy distribution in the wells. The activation energy of obtained from the QW green emission line indicated deepening of the localization of the carriers.

The kinetics of irreversible tensile stress development during annealing of dielectric films fabricated by plasma-enhanced chemical vapor deposition(PECVD) are studied, and the hypothesis of a rate-limiting hydrogen diffusion process is tested. Extra-long anneals with in situ stress measurements have been made: experimental observations on a silicon nitridefilm do not display the characteristics expected of stress development limited by diffusion. Nor do these data imply a limiting first-order reaction process. Infrared spectroscopy results indicate that the amount of bonded hydrogen decreases in proportion with the stress increase, strongly implying stress development is a result of the reduction of bonded hydrogen alone. These findings demonstrate that diffusion in PECVDfilms does not limit stress development; instead, it is likely governed by nonstraightforward kinetics of hydrogen bond breaking, which is followed by the rapid diffusion of product molecules.

Scanning capacitancemicroscopy and spectroscopy combined with numerical simulations have been used to image nanoscale electronic structures in quantum-well heterostructures grown by metalorganic chemical vapor deposition. Macroscopic capacitance–voltage spectroscopy and numerical simulations indicate that, depending on the bias voltage applied, either electron or hole accumulation in the -type quantum-well region can occur. Scanning capacitance microscope images reveal local variations in electronic properties with structure similar to that of monoatomic steps observable in surface topography. Scanning capacitancespectroscopy combined with numerical simulations indicates that the observed features correspond to variations in carrier concentration arising from monolayerfluctuations in the thickness of the subsurface quantum-well layer, with thickness variations occurring over distances of tens of nanometers to a micron or more.